Methods for measuring instantaneous crop yield as a grain harvester is moving through a field of grain have been the subject of both research studies and prior inventions. Methods for measuring either the volumetric flow rate or the mass flow rate of grain have been used to provide a grain flow rate signal which can be used to calculate either the total weight of grain harvested within a given field area or the instantaneous yield of the crop at the present location of the harvester in the field. These data are useful to the agricultural producer to allow measuring the effect of different soil conditions or crop growing practices on crop yield. Total weight of grain is calculated by integrating grain mass flow rate versus time. Instantaneous crop yield is calculated by dividing instantaneous grain mass flow rate by the instantaneous rate at which the harvester is harvesting the field area. For example, instantaneous grain mass flow rate in bushels per hour divided by instantaneous rate of harvesting the field area in acres per hour provides instantaneous crop yield in bushels per acre.
Numerous methods have been designed to measure the flow rate of grain on harvesters. However, none of the previous methods have been fully practical in terms of providing a simple method of continuously measuring grain mass flow rate while harvesting.
Impact type mass flow rate sensors for particulate or granular materials are well known in the art and are widely used in stationary installations such as material processing plants. Typical examples are disclosed in U.S. Pat. Nos. 3,640,135, 4,440,029 and 4,718,284, among others. All of these devices utilize the principle of creating a reaction force proportional to material mass flow rate by changing the velocity of a stream of granular material as it strikes an impact plate at a known initial velocity. Further, these devices are drop type sensors where granular material is dropped onto an impact plate from a known height above the plate. While providing the height required for a drop type sensor is very practical in many stationary applications due to large size of the associated processing equipment, providing sufficient drop height to obtain an accurate grain mass flow rate measurement on a harvester is much less practical.
U.S. Pat. No. 4,407,380 describes one of several types of devices which have been developed to measure flow rate of grain as it exits the outlet of the grain storage tank unloading auger of a harvester. However, use of such devices to continuously measure grain flow rate while harvesting is impractical, since such use would require continuous operation of the unloading auger of the harvester and movement of a grain hauling vehicle with the harvester throughout the field.
U.S. Pat. No. 4,765,190 describes a grain mass flow rate sensor which is installed at the outlet of the clean grain elevator of a harvester and utilizes the momentum of grain exiting the clean grain elevator to continuously measure grain mass flow rate during harvesting. However, this device is not an impact type sensor, since the speed of the grain is not significantly reduced by contact with the sensing plate. Instead, the curved sensor plate changes the direction of flow of the stream of grain, creating a centrifugal force which is measured. Although this sensor construction is used to minimize the effect of friction between grain and the sensing plate on the measured force, said construction is also more complex than that of a simple impact type mass flow rate sensor.
U.S. Pat. Nos. 4,063,456 and 4,719,805 recognize the need to compensate for the effect of variations in speed of granular material striking an impact plate, and thus propose means for measuring either the speed of the conveyor or of the granular material. While the systems disclosed in these patents can achieve high accuracy by compensating for speed variations, they both require additional sensing devices to obtain a speed measurement.
Since the agricultural producer receives payment for grain based on a standard trading moisture content, the weight of grain with moisture content exceeding the standard must be corrected to represent the weight of the grain after drying to standard moisture content. Therefore, to obtain maximum accuracy of measuring true crop yield, it is desired to provide means for automatically and continuously measuring moisture content of the grain as it is harvested. U.K. patent 2,087,704 describes means for automatically measuring moisture content of grain in conjunction with a device for measuring the volume rate of grain flow on a harvester. However, the proposed moisture measuring device is complex, because it requires the addition of a grain trapping chamber separate from the flow rate measuring means to insure exposure of a known amount of grain to the moisture measuring device.
Whatever the precise merits, features and advantages of the above cited devices, it will be seen that none of them provides all of the objects of the present invention.